In general, an induction motor is widely used as a power source of various types of equipment. In such type of electric motor, a power source voltage is supplied from a power trunk line to a primary winding provided in a stator to generate a rotation magnetic field. The rotation magnetic field causes a rotation torque in a rotor to rotate. In this case, harmonic voltages are generated due to the structure of the stator and the rotor. The harmonic voltages lower an operational efficiency of the electric motor, and lead to an increase in temperature.
Therefore, various proposals for lowering the harmonics have been made. For example, an element for suppressing a harmonic magnetic flux is provided in a part of a magnetic body where a main magnetic circuit of the electric motor is formed (for example, see Patent Literature 1).